The present invention is directed to the use of additives to depress (lower) the freeze point of aviation fuels. In particular, the present invention is directed to the use of specific additives to lower the freeze point of jet fuels.
The freeze point for aviation fuels is defined as the fuel temperature at which solid hydrocarbon crystals, formed on cooling, disappear when the temperature of the fuel is allowed to rise. The freeze point of aviation fuels is measured typically by the ASTM D2386-97, D5901-96 or D5972-96 test methods.
It is absolutely essential that aviation fuel have a freeze point sufficiently low to preclude interference with flow of fuel through filter screens to the engines at temperatures prevailing at high altitudes. The temperature of fuel in an aircraft fuel tank decreases at a rate proportional to the duration the flight. Therefore, the maximum freeze point allowed for the fuel is usually related to the type of flight. That is, long duration flights would usually require fuel of a lower freeze point than short duration flights. However, an exception to this general rule may occur during military combat operation where the aircraft are operated at a significant higher altitude. In this case, lower freeze point jet fuel may be required due to the higher altitude although the duration of the flight is typically shorter.
Various patents teach the addition of pour depressants to middle distillates, such as heating oils and diesel fuels, to improve their cold flow properties. For example, various polymers, useful as middle distillate pour point depressants prepared from ethylene, have been described in the patent literature. These pour depressants include copolymers of ethylene and vinyl esters of lower fatty acids such as vinyl acetate (U.S. Pat. No. 3,048,479); copolymers of ethylene and alkyl acrylate (Canadian Patent No. 676,875); terpolymers of ethylene with vinyl esters and alkyl fumarates (U.S. Pat. Nos. 3,304,261 and 3,341,309); polymers of ethylene (British Patent Nos. 848,777 and 993,744); chlorinated polyethylene (Belgian Patent No. 707,371 and U.S. Pat. No. 3,337,313). In addition, U.S. Pat. Nos. 5,092,908 and 3,883,318 teach the combinations of a pour depressant with a middle distillate which may include jet fuels to lower the pour point of the distillate.
However, typically low jet fuel freeze points are attained by changing the distillation cut points or component blending to produce a jet/aviation fuel having an acceptable freeze point. The present invention is directed to a chemical treatment of the aviation fuel which not only lowers the freeze point of the jet/aviation fuel beyond the freeze point obtained by blending alone, but also achieves this result at a substantially lower cost.
It is the primary object of the present invention to provide a novel jet fuel composition having a low freeze point with improved low temperature filterability.
It is another object of the present invention to provide a novel process for producing a low freeze point jet fuel with improved low temperature filterability.
Additional objects and advantages of the present invention will be set forth in the description which follows and, in part, will be obvious from the description or may be learned by the practice of the invention. The objects and advantages of the invention may be realized by means of the instrumentalities and combinations pointed out in the appended claims.
To achieve the foregoing object and in accordance with the purpose of the invention as embodied and broadly described herein, the improved aviation fuel composition of the present invention comprises a mixture of an aviation fuel and a compound selected from at least one member of the group consisting of
(1) the reaction product of an alkanol amine with a hydrocarbyl-substituted acylating agent wherein the hydrocarbyl group comprises a substantially linear alkyl or alkenyl group which contains an average of about 8 to about 50 carbon atoms; or
(2) the reaction product of (a) substantially linear hydrocarbyl-substituted phenol wherein the hydrocarbyl substituent contains an average of about 8 to about 40 carbon atoms with an aldehyde or a source thereof having between 1 to 10 carbon atoms; or
(3) an aromatic moieties containing from about 1 to 3 aromatic rings wherein the aromatic moieties contains up to three substituents substantially linear hydrocarbyl constituents having from about 1 to 50 carbon atoms and the aromatic moieties are coupled by alkylene groups having 1 to 100 carbon atoms; or
(4) an ethylene vinyl acetate copolymer having a number average molecular weight of between about 2,500 to 10,000 with a mole percent ethylene to vinyl acetate ratio of between about 65:35 to 85:15.
In a further aspect of the present invention, a process for lowering the freeze point of aviation fuel comprises adding to the aviation fuel in an amount sufficient to lower the freeze point of the aviation fuel a compound selected from at least one member of the group consisting of
(1) the reaction product of an alkanol amine with a hydrocarbyl-substituted acylating agent wherein the hydrocarbyl comprises a substantially linear alkenyl or alkyl group which contains an average of about 8 to about 50 carbon atoms; or
(2) the reaction product of (a) substantially linear hydrocarbyl-substituted phenol wherein the hydrocarbyl substituent contains an average of about 8 to about 40 carbon atoms with an aldehyde or a source thereof having between 1 to 10 carbon atoms; or
(3) an aromatic moieties containing from about 1 to 3 aromatic rings wherein the aromatic moieties contains up to three substituent substantially linear hydrocarbyl constituents having from about 1 to 50 carbon atoms and the aromatic moieties are coupled by alkylene groups having 1 to 100 carbon atoms; or
(4) an ethylene vinyl acetate copolymer having a number average molecular weight of between about 2,500 to 10,000 with a mole percent ethylene to vinyl acetate ratio of between about 65:35 to 85:15.
It should be understood that the term xe2x80x9csubstantially linear hydrocarbylxe2x80x9d generally means a linear content of at least 50%, preferably at least 75%, especially preferred being at least 90%.
In a preferred embodiment of the present invention, the aviation fuel is selected to be Jet Fuel A.
In another preferred embodiment of the present invention the aviation fuel is selected to be Jet Fuel A-1.
In still another preferred embodiment of the present invention the aviation fuel is selected to be Jet Fuel 8+100.